1, 3 Diphenylguanidine was nominated for testing by NCI because of the potential human exposure during production and use (rubber vulcanization) and because of lack of sufficient toxicity data for the guanidine class of chemicals. The objectives of the planned prechronic (14-day & 13-week) dosed feed studies in rats and mice are: 1. To characterize the toxicity associated with the repeated exposure to the chemical, the "no-effect-level", differences in sensitivity between sexes and species and the slope of the dose response curve. 2. To select the proper doses for use in a 2-year study to be designed for determining the carcinogenic potential of this chemical. The dosed feed route of administration was selected because human exposure could occur through this route and because the chemical is readily absorbed by rodents following consumption.